Heat treatment of nickel alloys

ABSTRACT

Heat treating process enables obtaining desired combinations of strength, ductility and fabricability characteristics in heat resistant age-hardenable alloys having precipitation-hardening amounts of columbium, titanium and/or tantalum in a nickelcontaining matrix.

nited States Patent Smith, Jr. et al.

[451 Mar. 18, 1975 1 HEAT TREATMENT OF NICKEL ALLOYS [75] Inventors:Darrell Franklin Smith, Jr.; Edward Frederick Clatworthy, both ofHuntington, W. Va.

[73] Assignee: The International Nickel Company,

Inc., New York, NY.

[22] Filed: Aug. 13, 1973 [21] Appl. No.: 387,944

[52] US. Cl 148/142, 148/31, 148/32.5, 148/162 [51] Int. Cl C22c 41/02,C22f1/10,C22c 39/20 [58] Field of Search l48/12.7, 142, 162, 32.5,148/124; 75/128 R, 128 G, 128 T, 171, 134

[56] References Cited UNITED STATES PATENTS 3,046,108 7/1962 Eiselstein75/171 3,048,485 8/1962 Bieber 148/162 X 3,146,136 8/1964 Bird et al.148/162 3,147,155 9/1964 Lamb et al 148/162 X 3,390,023 6/1968 Shiro148/127 3,575,734 4/1971 Muzyka et a1. 3,663,213 5/1972 Eiselstein eta1. 3,741,824 6/1973 Duvall et a1. 148/162 X Primary Examiner-C. Lovell[57] ABSTRACT Heat treating process enables obtaining desiredcombinations of strength, ductility and fabricability characteristics inheat resistant age-hardenable alloys having precipitation-hardeningamounts of columbium, titanium and/or tantalum in a nickel-containing matrlx.

8 Claims, N0 Drawings HEAT TREATMENT OF NICKEL ALLOYS The presentinvention relates to age-hardenable nickel alloys and more particularlyto heat treatment of nickel alloys, including nickel-iron-chromiumalloys strengthened with columbium and titanium.

Age hardenable alloys based on nickel and/or iron and containingprecipitation hardening amounts of titanium and/or columbium, andpossibly with aluminum or other precipitation hardening elements, havebeen known and used for many years. Often, the alloys are strengthenedwith heat treatments comprising annealing or solution treating at hightemperatures such as l,700F. or 2,100F. or higher, cooling rapidly downfrom the solution temperature to room temperature, e.g., air cooling orwater quenching, and thereafter reheating at lower temperatures ofaround l,lF. to l,400F. to precipitation harden the alloys.Precipitation-strengthened alloys containing chromium are often used forcomponents of gas turbines, e.g., turbine blades and turbine rotordiscs. For instance, one of the relatively recent additions to thefamily of nickel-ironchromium age-hardenable alloys is described in US.Pat. No. 3,663,213.

While very substantial progress has been accom plished is providinghigh-strength age-hardened alloy articles, needs for improvements arecontinually arising. Greater strength, particularly includingstressrupture strength and yield strength, are frequently desired andspecial characteristics, e.g., resistance to low cycle fatigue, havebecome of increased importance. Ductility requirements are practicallyalways present and experience with known alloys often brings forth needsfor special improvements, e.g., notch ductility or capability forspecially required elongation or reduction of area characteristics at aspecial temperature. Among other special needs are weldability,maintenance of required shape and size without distortion, resistance tohigh cycle fatigue, e.g., rotating beam load, corrosion resistance(including oxidation resistance), impact strength and stability afterlong time exposure in service. Improvements in the processing of knownalloys are particularly desired for obtaining specially neededcombinations of such important metallurgical characteristics and forfacilitating production of desired articles and structures with use ofpresently available alloys. And, of course, process improvements in thepresent can become highly beneficial for enhancing the characteristicsof future alloys.

In the present invention there has been discovered a process for heattreatment of age-hardenable nickelcontaining alloys to provide articleshaving desired combinations of strength, fabricability and ductility, orother desired characteristics, in the heat treated condition.

It is an object of the present invention to provide a process for heattreating age-hardenable nickel alloys.

Other objects and advantages of the invention will become apparent fromthe following description.

The present invention comtemplates a process for heat treating anage-hardenable heat-resistant nickel alloy containing precipitableamounts of gamma-prime forming metal selected from the group consistingof columbium, titanium and tantalum comprising: heating the alloy at atemperature in the gamma-prime solid solution range of the alloy andobtaining the alloy in'the solid solution condition having precipitableamounts of the gamma-prime forming metal in solid solution; cooling thealloy down to the gamma-prime solvus temperature; then slowly coolingthe alloy uniformly at a controlled cooling rate not greater than 500F.per hour, e.g., about 20F. per hour to 500F. per hour, from thegamma-prime solvus temperature down to at least about L00F. below thegamma-prime solvus temperature, thus into precipitation temperaturerange of the alloy; heat treating the slow-cooled alloy at an uppertemperature in the precipitation range to precipitate coarse particlesof gamma-prime at (in the vicinity of) the grain boundaries of the alloyand dispersed uniformly within the grains while retaining a portion ofthe gamma-prime forming metal in solution; thereafter heat treating thealloy at a lower temperature in the precipitation hardening range toprecipitate fine particles of gamma-prime dispersed uniformly within thegrains; and then cooling the alloy to room temperature, therebyproviding a precipitation hardened alloy having coarse particles ofgamma-prime at the grain boundaries and having coarse gamma-primeparticles and fine gamma-prime particles dispersed uniformly within thegrains. The process may also precipitate the delta and eta equilibriumphases (Ni Cb and Ni -,Ti) in the grain boundaries.

When carrying the invention into practice, the slow cooling rate shouldbe controlled sufficiently to avoid having the alloy at high elevatedtemperature for excessively long periods of time that would result indetrimental grain growth or excessive overaging. And, of course,production economy negates extending the heat-treatment time beyondbenefit. Accordingly, for most purposes the slow-cooling rate should beat least about 20F. per hour (F/Hr) and is advantageously at least50F/Hr.

The age-hardenable heat-resistant nickel alloys treated in the processof the. invention comprise, by weight, at least 2% metal from the groupconsisting of columbium, titanium and one-half the wt; of any tantalum,at least about 25% nickel, up to 60% iron with a total of at least 50%nickel-plus-iron, and are characterized by a solidus temperature of atleast about 2,300F. Nickel is required for providing, inter alia,stability to the microstructure, including a stable austenite matrix; ifthe alloy does not contain sufficient nickel, detrimental phases, e.g.,sigma, may be formed. Substantial amounts of chromium, e.g., 8% oradvantageously 12% or more for corrosion resistance, can be present inthe alloy. Small amounts of aluminum, e.g., 0.3% or 3% aluminum, may bepresent and can be beneficial for strength, ductility and/or oxidationcharacteristics. Thus, the process includes heat treatment ofage-hardenable nickel-iron-chromium alloys, e.g., heat resistant alloyscontaining about 40% nickel, 40% iron, 15% chromium, 3% columbium, 1.7%titanium and 0.3% aluminum.

The gamma-prime of the particles precipitated in the heat treatment isthe Ni (Cb,Ta,Ti)' gamma-prime precipitate, which may also compriseother elements such as aluminum, e.g., Ni (Cb,Ti,Al). The solutiontemperatures are sufficiently high for enabling precipitable amounts ofcolumbium, tantalum and/or titanium to enter into solid solution inpractical solution treating times, e.g. /2 hour or 8 hours. Somecolumbium or titanium or other elements may be retained, possibly ascarbides, without solution. Most of the solution temperatures are in arange of about 1,600F. to l,950F.

Advantageously for high temperature strength, the solution treatment isat 1,625F. to 1,700F. when the columbium-plus-titanium-plus-Vz tantalumcontent is 4% to 5.5% and is at 1,700F. to 1,800F. when thecolumbium-plus-titanium-plus-V2 tantalum content is 5.7% to 6.7%, andthe time is sufficient to obtain a homogenous gamma phase solution,e.g., one-half hour or more. Herein, percentage summations of tantalumplus other gamma-prime forming elements, the weight percentage oftantalum present is multiplied by one-half (in view of the relativelyhigh atomic weight of tantalum). The precipitation-hardening temperaturerange spans the temperature at which, for most commercial practices,strengthening precipitates of the gamma prime can be precipitated in thealloy, e.g., 4 hours to 48 hours at l,lF. to 1,800F. Advantageously, thecoarse particles are precipitated in the upper one-third of the rangeand the fine particles are precipitated in the lower half of the range.The upper precipitation may be accomplished, and the coarse particlesprecipitated, by slow cooling through the precipitation range, providedthat sufficient dissolved gamma-prime is retained for subsequentlyprecipitating the fine particles.

Generally, the present process precipitates essentially all of thedissolved columbium, titanium and tantalum, with at least about (byvolume) of the gamma-prime in the coarse particle form and at leastabout 20% of the gamma-prime in the fine particle form. Inasmuch asessentially all of the gamma prime is precipitated when the process iscomplete, the process provides advantages of microstructural stability.Forms of the gamma-prime particles include plate-like, globular, andcubic shapes. The coarse particle sizes can be from about 0.04 to 1micron and the fine particle sizes can be up to 0.1 micron, dependingupon alloy composition. In the same alloy, the coarse particles are atleast twice, usually five or ten times, the size of the fine particles.With a nickel-chromium-iron alloy composition containing not more than2.5% aluminum-plustitanium and at least 2.5% columbium, good resultswere obtained by precipitating coarse particles of 0.04 to 0.1 micronsize and fine particles of sizes up to 0.02 microns.

Good results have been obtained with special embodiments wherein, inaccordance with the invention, the alloy is cooled slowly from the solidsolution'temperature down through the precipitation range and thereafterreheated for one or more treatments in the precipitation range tocomplete the gamma-prime precipitation. For instance,nickel-iron-chromium alloys containing 4% to 5.3%columbium-plus-titanium are cooled slowly, at rates in the range of50F/Hr to 500F/Hr, from solid solution temperatures in the range of1,625F. to 1,950F., down to l,l0OF. or lower and thereafter reheated atleast once in the range of 1,100F. to 1,625F. to finish precipitation.

An important feature of the invention is the provision of specialembodiments whereby special benefits are achieved with heat treatmentsaccording to advantageously restricted ranges. Thus, advantageously longstress-rupture life in combination with good short-time tensile strengthand ductility and good fabricability for welding or brazing are achievedwith a triple-stage heat treatment of an age-hardenablenickel-iron-chromium alloy containing titanium, columbium, and aluminumaccording to a triple-stage treatment comprising: heating to a solidsolution condition at least about 1,750F.

or higher; slow-cooling at a rate of about 50F/Hr to 500F/Hr from thesolid solution temperature to below the precipitation hardening range,e.g., slow-cooling to 1,10'OF., and then cooling to room temperature atany desired rate, e.g., air cooling; reheating at an intermediatetemperature of about 1,450F. to about 1,625F. for about 1 Hr. to 24 Hrs.and cooling to room temperature at any desired rate; and reheating to aprecipitation temperature of about 1,275F. to 1,425F. and holding withinthis range for about 1 to 24 Hrs., cooling at a controlled rate of about20F/Hr to 200F/Hr to a lower precipitation range of l,lO0F. to 1,200F.and holding in this lower range for a total aging time of about 5 Hrs.to 24 Hrs. and thereafter cooling to room temperature at any desiredrate.

Another embodiment, which is referred to herein as a twostage treatment,achieves good stress-rupture life and tensile strength andadvantageously high ductility and also has advantages of productioneconomy and fabricability with heat treatment of an age-hardenablenickel-iron-chromium alloy containing titanium, columbium and aluminumcomprising: heating to a solid solution condition at a temperature ofabout ],675F. or higher; slow-cooling at a rate of 250F/Hr to 350F/l-lrfrom the solid solution temperature down through theprecipitation-hardening range, e.g., down to l,100F., and then down toroom temperature at any desired rate; and reheating to a precipitationtemperature of about l,275 F. to l,425F. and holding within this rangefor about 1 to 24 Hrs., cooling at a controlled rate of about 20F/l-lrto 200F/Hr to a lower precipitation range of about 1,100F. to 1,200F.and holding in this lower range for a total aging time of about 5 Hrs.to 25 Hrs. and thereafter cooling to room temperature at any desiredrate.

The foregoing two-stage and three-stage treatments referred to inconnection with nickel-iron-chromium alloys containing titanium,columbium and aluminum particularly applicable in the heat treatment ofagehardenable nickel-iron alloys containing (in weight percentages)about 39% to 44% nickel, 14.5% to 17.5% chromium, 1.5% to 2% titanium,2.5% to 3.3% columbium, 0.05% to 0.4% aluminum, up to 0.06% carbon, upto 0.35% manganese, up to 0.35% silicon, up to 0.006% boron and balanceessentially iron. For treating alloys in this range, and possibly otheralloys, heating three hours at 1,550F. is recommended for theintermediate stage in three-stage embodiments of the invention and,also, a procedure of heating eight hours at 1,325F., furnace cooling atF/Hr to 1,150F. and holding eight hours at l,l50F. is recommended forthe precipitation stage in two-stage or three-stage embodiments of theinvention.

It is contemplated that the heat treatment of the invention is generallyapplicable for improving the metallurgical characteristics, or obtainingat least acceptable strength and ductility characteristics whileavoiding detrimental effects of more rapid cooling from solutiontemperature, e.g., embrittlement, cracking, warping or other structuraldistortion, in processing of agehardenable nickel alloys containing atleast about 25% nickel, up to 60% iron, with a total of at least 50%nickel-plus-iron, up to 6.5% columbium and up to 5% titanium, up to 6%tantalum, with a total of at least 2%columbium-plus-titanium-plus-b-tantalum, up to 6.5% aluminum, providedthe total of columbium, titanium, tantalum and aluminum does not exceed10%, up to 2% vanadium, up to 25% chromium, advantageously 12% to 25%chromium, up to 30% cobalt, up to molybdenum or tungsten or mixturesthereof and up to 0.2% each of boron, zirconium and carbon. Either thenickel, or the iron when present, may be considered as the balance.

For the purpose of giving those skilled in the art a betterunderstanding of the practice and advantages of the invention, thefollowing illustrative examples are given.

EXAMPLE I A nickel-iron alloy that had been hot rolled to ninesixteenthsinch diameter bar was obtained in the hotrolled condition. Analyzedchemical composition of the alloy (Alloy 1) was 41.92% nickel, 16.28%chromium, 2.96% columbium, 1.90% titanium, 0.33% aluminum, 0.03% carbon,0.003% boron, 0.14% manganese, 0.04% silicon, 0.01% copper, 0.001%sulfur and balance iron. (Percentage amounts of columbium referred toherein may include small incidental amounts of tantalum.) A specimen(Specimen 1) of the bar of alloy 1 in the hot-rolled condition washeated to the solid-solution condition by heating one hour at 1,800F.and was then slowly cooled directly from the 1,800F. solid-solutiontemperature down to 1,100F. at a slow cooling rate of 280F/Hr; then thespecimen was air cooled to room temperature. Next, in the presentexample of a two-stage embodiment of the invention, specimen 1 wasprecipitation heat treated at 1,325F. for 8 hours, furnace cooled at arate of 100F/1-1r to 1,150F., for 8 Hrs. and then air cooled to roomtemperature. Metallurgical examination of the thus heattreated specimen1 showed the heat treatment had precipitated gamma-prime as coarseparticles of about 3 (UTS), tensile elongation as percent along 10inchgage length (E1) and reduction of area across .252 inch EXAMPLE 11l0-solution temperature to 1,100F. at the following coolfing rates: 11-1at 50F., 11-2 at 100F/Hr; 11-3 at 200F/1-1r and 11-4 at 500F/Hr; allwere air cooled from l 1,100F. to room temperature. Thereafter,specimens 511-1, 11-2, 11-3 and 11-4 were reheated to an intermediatetreatment temperature of 1,550F. for,3 Hrs. and air fcooled to roomtemperature and were then precipitaition heat-treated by heating at1,325F. for 8 Hrs., furinace cooling at 100F/Hr down to 1,150F. andholding ."at 1,150F. for 8 Hrs., which was followed by air cooling toroom temperature. All four of the triple-stage heat-treated specimenshad intra-granular dispersions jof coarse particles and fine particlesof gamma-prime. jResults of short-time tensile tests and stress-rupture-tests conducted by standard practices (in accord with Example 1) on theheat-treated alloy products resulting from the four triple-stageembodiments in the present Example are set forth in Table I.

The heat treated conditions produced in Examples 1 g and 11 were allcharacterized by good machinability, as confirmed by machining ofthreaded test bars.

Also shown in Table l are the results of comparable testing of the samealloy composition when treated by two different heat treatments, A andB, that are contrary to the invention. Two other specimens, A and B, ofthe nine-sixteenth-inch diameter hot rolled bar stock of alloy 1 wereheat treated by solution treating one hour at 1,800F. and air cooling toroom temperature (which caused an average cooling rate of about 22,250F.per hour between 1,800F. and 1,100F). Then, in treatment A theair-cooledalloy was further treated according to the precipitation heattreatment that followed the slow cooling of Specimen 1 in Example 1, andin treatment B the air-cooled alloy was fur-' ther treated according tothe intermediate and precipitati on treatments that followed the slowcooling of the specimens in Example 11.,

TABLE 1 Short-Time Tensile Tests Stress-Rupture Tests Smooth BarCombination Smooth/Notch Bar Room Temperature 1200F. 105 Ksi at 1200F.Treat- YS, UTS, El, RA, YS, UTS, E1, RA Life El, RA, Fracture ment CoolRate Age* ksi ksi ksi ksi Hr. 71 Location 1 280F/Hr 1 159.0 195.5 20 39121.0 141.0 31 60 94.4 14 31 Smooth Section 11-1 50F/Hr 2 147.0 185.5 1724 126.0 144.0 22 37 138.3 18 37 do. 11-2 100F/Hr 2 150.5 186.0 17 26129.0 145.0 24 42 136.8 18 38 do. "-3 200F/Hr 2 150.5 190.5 18 24 128.5147.0 24 43 138.5 18 44 do. "-4 500F/Hr 2 146.0 185.0 18 125.0 143.5 28131.8 22 40 do.

A Air Cool 1 159.0 185.5 25 49 123.0 146.0 30 1.8 Notch Section B AirCool 2 154.0 186.0 19 31 123.0 141.0 30 56 77.5 18 48 Smooth Section Age(1)1325F. for-8 Hrs., Furnace Cool at F/Hr to l F. and hold for 8 Hrs.at ll50"F., then Air Cool to room temperature.

Age (2)l550F. for 3 Hrs., Air Cool, plus 132SF. for 8 Hrs., Furnace Coolat 100F/Hr to 1150F and hold for 8 Hrs. at 1150F. then Air Cool In roomtemperature.

diameter gate section (RA) and stress-rupture test results of life inhours, elongation and reduction of area are set forth in the followingTable 1. Stress-rupture test result were obtai e d w it h a rn oothsection diameter characteristics. Also, this example wherein the rate ofcooling from solid solution was controlled within a range of 250F/Hr to350F/Hr provides a good combination of tensile strength, stress-rupturestrength and ductility and offers the production economy of the shortertwo-stage treatment. Turning to treatment II, it is evident thatsuperior stress-rupture life along with desirable levels of tensilestrength and ductility was obtained with the three-stage treatment,especially with cooling rates of 100F/Hr to 200F/Hr.

Treatment A failed to provide satisfactory notch ductility inasmuch'asthe stress-rupture test specimen fractured in thc notched section aftera very short life at l200F.

While the invention has been exemplified herein with the specificcomposition of alloy 1, it is contemplated that the heat treatment beperformed with many other alloys having compositions within rangesherein provided and be beneficial for obtaining improved metallurgicalcharacteristics, particularly including advantageously good ductility,and also enhanced stressrupture life and other desirable characteristicsmentioned hereinbefore. For instance, the invention is consideredapplicable in heat treatment of alloys 2 to 21 'having the nominalcompositions set forth, below the nominal composition of alloy 1, in thefollowing Table ll.

61611 16561111111111 1116 511111111 111111110 111 of 11115 invention andappended claims.

We claim:

1. A process of heat treating an age-hardenable heatresistant nickelalloy consisting essentially of at least about 25% nickel and up to 60%iron, with a total of at least 50% nickel-plus-iron, and precipitableamounts of gamma-prime forming metal selected from the group consistingof up to 6.5% columbium, up to titanium and up to 6% tantalum andmixtures thereof with a total of at least 2%columbium-plus-titanium-plus-Vz tantalum up to 6.5% aluminum, the totalof the columbium content plus the titanium content plus the aluminumcontent plus one-half the tantalum content does not exceed up to 2%vanadium, up to chromium, up to cobalt, up to 10% molybdenum, tungstenor mixtures thereof, up to 0.2% boron, up to 0.2% zirconium and up to0.2% carbon and characterized by a solidus temperature of at least about2,300F., a gamma-prime solvus temperature of at least 1600F. and agamma-prime precipitation temperature of at least l 100 F. comprising:

a. heating the alloy at a temperature of about 1,600 to 1,950F andgamma-prime solid solution range of the alloy and obtaining the alloy inthe solid solution condition having precipitable amounts of the TABLE llNominal Compositions, Weight Percent Alloy C Mn Si Cr Co Mo' Cb Mg Ti AlB Zr Fe Ni 2 0.05 0.1 0.1 12 5.7 2.8 0.2 0.015 Bal. 42

7 0.04 0.6 0.2 15 2.4 0.6 6.5 Bal.

9 0.15 0.5 0.5 20 1-0 10.0 2.6 1.0 0.005 Bal.

10 0.06 0.1 0.7 20 1 2.5 1.3 Bal. 11 0.07 0.5 07 20 I8 2.4 1. 1 Bal. 120.09 19 11 10.0 3.1 1.5 0.005 Bal. 13 0.02 5 2.5 0.6 0.005 B111. 42 140.03 15 3.0 1.4 0.6 0.008 Bal. 38 15 0.08 18 18 4.0 2.9 2.9 0.006 0.05Bal. 16 0.05 19 12 6.0 1.0 3.0 2.0 4 0.005 Bal. 17 0.08 15 18 5.2 3.54.3 0.030 Hal. [8 0.08 19 13 4.3 3.0 1.3 0.006 0.006 Bal. 19 0.06 15 155.3 3.5 4.4 0.03 57 20 0.10 20 20 3.0 2.0 B111. 21 0.04 0 70 0 3 15 0.92.5 0.8 6.8 Bal.

The present invention is particularly applicable in the gamma-primeforming metal in Solid Sol t o b. production of nickel-iron alloyproducts and articles cooling the alloy from the solid solutiontemperafor use where strength and ductility are required in ture down tothe gamma-prime solvus temperature; structures, includng weldedstructures, engines and c. then slowly cooling the alloy uniformly at aconother machines, and in articles, including components trolled coolingrate of at least about 20F. per hour of machines, e.g., gas turbineblades, and is specially and not greater than 500F. per hour from thegam applicable for overcoming distortion difficulties that ma-primesolvus temperature down to about may otherwise arise when heat treatinglarge or com- 1,100F or lower; plex structures and articles, e.g.,turbine rotor discs. d. heat treating the slow-cooled alloy at an upperAmong other things, the invention is useful in the protemperature in theprecipitation range to precipiduction of turbine shafts and cases,diffuser cases, comtate coarse patches of gamma-prime in the vicinitypressor discs and shafts and fasteners. of the grain bounderies of thealloy and dispersed Although the present invention has been described inuniformly within the grains while retaining a porconjunction withpreferred embodiments, it is to be untion of the gamma-prime formingmetal in solution; derstood that modifications and variations may beree. thereafter heat treating the alloy at a lower tempersorted towithout departing from the spirit and scope of the invention, as thoseskilled in the art will readily understand. Such modifications andvariations are considature in the precipitation hardening range toprecipitate fine particles of gamma-prime dispersed uniformly within thegrains; and

f. then cooling the alloy to room temperature, to

thereby provide the alloy in the heat treated condition characterized byhaving coarse gamma-prime particles at least twice the size of the finegammaprime particles.

2. A process as set forth in claim 1 wherein the alloy is slowly cooledfrom the solid-solution temperature down through the precipitationhardening temperature range at a slow-cooling rate in the range of 50F.per hour to 500F. per hour.

3. A process as set forth in claim 2 wherein the slowcooling rate is inthe range of 100F. per hour to 200F. per hour.

4. A process as set forth in claim 2 wherein the slowcooling rate is inthe range of 250F. per hour to 350F. per hour.

5. A process as set forth in claim 1 wherein, after the alloy isslow-cooled to at least 100F. below the gamma-prime solvus temperature,the reheating at an upper temperature is at about 1,450F. to about1,625F. for about 1 to 24 hours and the reheating at a lower temperatureis accomplished by reheating at about 1,275F. to l,425F. for about 1 to24 hours, then cooling at a rate of about F. per hour to 200F.

per hour to a range of about 1,100F. to 1,200F. and holding at about1,,100F. to |,200F. for at least 5 hours.

6. A process as set forth in claim 1 wherein, the solid solutiontemperature is at least about 1,675F., the alloy is slow cooled from thesolid solution temperature down through the precipitation hardeningtemperature at a rate in the range of 250F. per hour to 350F. per hourand is thereafter further heat treated by reheating at about 1,275F. tol,425F. for about I to 24 hours, then cooling at a rate of about 20F.per hour to 200F. per hour to a range of about l,lO0F. to 1,200F. andholding at about l,l00F. for at least 5 hours.

7. A process as set forth in claim 1 wherein the alloy contains about39% to 44% nickel, 14.5% to 17.5% chromium, 1.5% to 2% titanium, 2.5%to3.3% columbium, 0.05% to 0.4% aluminum, up to 0.06% carbon, up to0.35% manganese, up to 0.35% silicon, up to 0.006% boron and balanceessentially iron.

8. A process as set forth in claim 7 wherein the coarse particles areprecipitated with sizes of 0.04 microns to 0.1 microns and the fineparticles are precipitated with sizes of up to 0.02 microns.

INETED STATES PATENT OFFICE QER'IIFICATE 0F CORREQTION 9 PATEN! NO.318711928 DATED March 18, 1975 iNVENTORkS) Darrell Franklin Smith,Jr.and Edward Frederick Clatw-orthy H is certrfied that error appears inthe above-identified patent and that sard Letters Patent 0 are herebycorrected as shown below:

Col. 1, line 26, for "is" read ----in--.

C01. 3, line 8, insert the word "in" before the word "percentage".

, Col. 4, line 38, insert the Word are after the word "aluminum" Col. 6,line ll, for read Col. 8, line 25 (line 21 of claim 1) insert "in the"after the word and".

Line 57 (line 35 of claim. 1) f r "or read --and--.

Line 60 (line 38 of claim 1) for "patches" read "particles",

Col. 10, line 13 (line 10 of claim 6) after "l,lO0F." insert -tol200F.-.

Signed and Sealed this 9 twenty-sixth Day Of August 1975 [SEAL] Arrest.-

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner njlalenrsand Trademarks

1. A PROCESS OF HEAT TREATING AN AGE-HARDENABLE HEATRESISTANT NICKELALLOY CONSISTING ESSENTIALLY OF AT LEAST ABOUT 25% NICKEL AND UP TO 60%IRON, WITH A TOTAL OF AT LEAST 50% NICKEL-PLUS-IRON, AND PRECIPITABLEAMOUNTS OF GAMMA-PRIME FORMING METAL SELECTED FROM THE GROUP CONSISTINGOF UP TO 6.5% COLUMBIUM, UP TO 5% TITANIUM AND UP TO 6% TANTALUM ANDMIXTURES THEREOF WITH A TOTAL OF AT LEAST 2%COLUMNIUMPLUS-TITANIUM-PLUS-1/2 TANTALUM UP TO 6.5% ALUMINUM, THE TOTALOF THE COLUMBIUM CONTENT PLUS THE TITANIUM CONTENT PLUS THE ALUMINUMCONTENT PLUS ONE-HALF THE TANTALUM CONTENT DOES NOT EXCEED 10%, UP TO 2%VANDIUM, UP TO 25% CHROMIUM, UP TO 30% COBALT, UP TO 10% MOLYBDENUM,TUNGSTEN OR MIXTURES THEREOF, UP TO 0.2% BORON, UP TO 0.2% ZIRCONIUM ANDUP TO 0.2% CARBON AND CHARACTERIZED BY A SOLIDUS TEMPERATURE OF AT LEASTABOUT 2,300*F., A GAMMA-PRIME SOLVUS TEMPERATURE OF AT LEAST 1600*F. ANDA GAMMA-PRIME PRECIPITATION TEMPERATURE OF AT LEAST 1100*F. COMPRISING:A.HEATING THE ALLOY AT A TEMPERATURE OF ABOUT 1,600 TO 1,950*F ANDGAMMA-PRIME SOLID SOLUTION RANGE OF THE ALLOY AND OBTAINING THE ALLOY INTHE SOLID SOLUTION CONDITION HAVING PRECIPITABLE AMOUNTS OF THEGAMMA-PRIME FORMING METAL IN SOLID SOLUTION, B. COOLING THE ALLOY FROMTHE SOLID SOLUTION TEMPERATURE DOWN TO THE GAMMA-PRIME SOLVUSTEMPERATURE; THEN SLOWLY COOLING THE ALLOY UNIFORMLY AT A CONTROLLEDCOOLING RATE OF AT LEAST ABOUT 20*F. PER HOUR AND NOT GREATER THAN500*F. PER HOUR FROM THE GAMMA-PRIME SOLVUS TEMPERATURE DOWN TO ABOUT1,100*F OR LOWER, D.HEAT TREATING THE SLOW-COOLED ALLOY AT AN UPPERTEMPERATURE IN THE PRECIPITATION RANGE TO PRECIPITATE COARSE PATCHES OFGAMMA-PRIME IN THE VINCINITY OF THE GRAIN BOUNDERIES OF THE ALLOY ANDDISPERSED UNIFORMLY WITHIN THE GRAINS WHILE RETAINING A PORTION OF THEGAMMA-PRIME FORMING METAL IN SOLUTION; E.THEREAFTER HEAT TREATING THEALLOY AT A LOWER TEMPERATURE IN THE PRECIPITATION HARDENING RANGE TOPRECIPITATE FINE PARTICLES OF GAMMA-PRIME DISPERSED UNIFORMLY WITHIN THEGRAINS, AND F. THEN COOLING THE ALLOY TO ROOM TEMPERATURE, TO THEREBYPROVIDE THE ALLOY IN THE HEAT TREATED CONDITION CHARACTERIZED BY HAVINGCOARSE GAMMA-PRIME PARTICLES AT LEAST TWICE THE SIZE OF THE FINEGAMMA-PRIME PARTICLES.
 2. A process as set forth in claim 1 wherein thealloy is slowly cooled from the solid-solution temperature down throughthe precipitation hardening temperature range at a slow-cooling rate inthe range of 50*F. per hour to 500*F. per hour.
 3. A process as setforth in claim 2 wherein the slow-cooling rate is in the range of 100*F.per hour to 200*F. per hour.
 4. A process as set forth in claim 2wherein the slow-cooling rate is in the range of 250*F. per hour to350*F. per hour.
 5. A process as set forth in claim 1 wherein, after thealloy is slow-cooled to at least 100*F. below the gamma-prime solvustemperature, the reheating at an upper temperature is at about 1, 450*F.to about 1,625*F. for about 1 to 24 hours and the reheating at a lowertemperature is accomplished by reheating at about 1,275*F. to 1,425*F.for about 1 to 24 hours, then cooling at a rate of about 20*F. per hourto 200*F. per hour to a range of about 1,100*F. to 1,200*F. and holdingat about 1,100*F. to 1, 200*F. for at least 5 hours.
 6. A process as setforth in claim 1 wherein, the solid solution temperature is at leastabout 1,675*F., the alloy is slow cooled from the solid solutiontemperature down through the precipitation hardening temperature at arate in the range of 250*F. per hour to 350*F. per hour and isthereafter further heat treated by reheating at about 1,275*F. to1,425*F. for about 1 to 24 hours, then cooling at a rate of about 20*F.per hour to 200*F. per hour to a range of about 1,100*F. to 1,200*F. andholding at about 1,100*F. for at least 5 hours.
 7. A process as setforth in claim 1 wherein the alloy contains about 39% to 44% nickel,14.5% to 17.5% chromium, 1.5% to 2% titanium, 2.5% to3.3% columbium,0.05% to 0.4% aluminum, up to 0.06% carbon, up to 0.35% manganese, up to0.35% silicon, up to 0.006% boron and balance essentially iron.
 8. Aprocess as set forth in claim 7 wherein the coarse particles areprecipitated with sizes of 0.04 microns to 0.1 microns and the fineparticles are precipitated with sizes of up to 0.02 microns.